The disclosure relates generally to systems and methods for loading mandrels in collars of downhole tools. Wellbores (also known as boreholes) are drilled to penetrate subterranean formations for hydrocarbon prospecting and production. During drilling operations, evaluations may be performed on the subterranean formation for various purposes, such as to locate hydrocarbon-producing formations and manage the production of hydrocarbons from these formations. To conduct formation evaluations, the drill string may include one or more drilling tools that test and/or sample the surrounding formation, or the drill string may be removed from the wellbore, and a wireline tool may be deployed into the wellbore to test and/or sample the formation. These drilling tools and wireline tools, as well as other wellbore tools conveyed on coiled tubing, drill pipe, casing or other conveyers, are also referred to herein as “downhole tools.” Downhole tools may be made up of individual collars that are connected together, for example, by threaded connections, to form the tool. The collars may house one or more modules designed to provide functionality, such as power, telemetry, pressure testing, and sampling, among others. The modules may be made up of one or mandrels that are subjected to axial shock, vibration, and thermal expansion. To minimize these effects, the modules may be loaded in compression with an axial load device (ALD) in the collar.